Considering the labor involved, I wouldn't try an aftermarket Evap unless it's you doing the work and you won't mind doing it again soon if the gamble doesn't work. To my knowledge, no one knows just how long any aftermarket evap will last in comparison. I've also never seen or heard of a copper evap (or ANY copper AC part) and I've been in the bus. for 25 yrs now. Copper heater cores, yes but never a copper evap. A copper evap might not absorb heat well or last as long as aluminum in that application. If you're paying someone else for labor (likely), I wouldn't gamble.
If you want it to last longer, replace the accumulator too with the Evap. That device absorbs moisture and becomes saturated (useless) if ever exposed to air for more than 20 minutes.